Authorities are trying to determine the motive for an attack in which a Missouri State University instructor is charged with fatally stabbing a retired professor.

Springfield police Capt. Vance Holland said Thursday that police believe they understand what happened in the attack that killed Marc Cooper, 66, and injured his wife, Nancy, The Springfield News-Leader reported. But he added that authorities are “still piecing together the why.”

Edward Gutting, 43, of Springfield was charged Thursday with second-degree murder, assault, burglary and armed criminal action. He is jailed on $1 million bond. No attorney is listed for him in online court records.

A probable cause statement said Marc and Nancy Cooper were sitting inside their home in an affluent Springfield neighborhood Wednesday night when Gutting came in through the back door wielding a large knife. Gutting chased Marc Cooper through the kitchen into the living room, knocked him down and stabbed him to death, according to the statement.

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Nancy Cooper was also cut several times as police say she tried to fight with Gutting. The statement said Gutting told Nancy Cooper at one point “it was between him and Cooper,” and he didn’t want to kill her — but he would if he had to.

Nancy Cooper was eventually able to call for help, and Gutting was arrested after officers found him walking in the street outside of the Cooper residence covered in blood, according to the statement.

Holland said Cooper and Gutting knew one another, but he could not say if they were friends.

Missouri State issued a statement saying Cooper was an emeriti history professor, and Gutting is an instructor of modern and classical languages. The university said Gutting, who has worked at the university since 2011, has been placed on administrative leave pending the outcome of this investigation.

Cooper, Gutting and Gutting’s wife, Angela Hornsby-Gutting, worked in the history department together from 2011-2014, according to a Missouri State spokeswoman. A bond recommendation from prosecutors said Hornsby-Gutting is not cooperating with police. She doesn’t have a listed phone number.

Ray Weiner, president of the Temple Israel, a Jewish synagogue in Rogersville where Cooper was an active member, described the victim as a friendly, soft-spoken man who would sometimes lead services when the rabbi was out of town.

“It’s hard to imagine anybody having a conflict with him,” Weiner said. “He came across as a very caring person in every dealing that I had with him.”